Planting Instructions by Flower Name
- Hardy Zones: 8-10
- Spacing: 10-15"
- Height: 15-20"
- Blooms: summer to fall
Dahlias are tender plants native to Mexico and in the daisy family, Asteraceae. Their flowers range widely in size, color, shape, and number of petals, making dahlias among the most diverse flowers, with thousands of varieties. They make excellent cut flowers.
Plant tubers outside after all chance of frost has passed. Plant 3-4” deep in a sunny location in rich, well-drained soil. Spacing requirements differ for each variety—see above. Dahlias take 2 to 2 ½ months to begin flowering. You may give them a jump by starting them indoors in gallon containers. Plant the tubers 4-6 weeks before the last frost date in potting mix. Keep in a warm, bright spot (60-75°F) and keep the soil barely moist until sprouts appear. Transfer to the garden when all danger of frost has passed, disturbing the roots as little as possible. For best results, plant dahlia tubers in groups of at least three of the same variety.
Larger varieties, such as Lilac Time, require support. Insert a stake or flower support as you plant the tubers in the ground, to avoid damaging the planted tubers later.
Smaller varieties, such as Mignon and Border dahlias, can be planted in window boxes or containers 12” or more in diameter. Space the tubers 8-10” apart when planting in containers.
Dahlias are heavy feeders and require plenty of water and fertilizer. Feed weekly with a liquid fertilizer until flower buds appear and be sure to keep soil moist. Dahlias are sensitive to drought and may not bloom if they are allowed to dry out. Mulch around the plants to retain moisture. Remove spent flowers to encourage continued blooming.
If bushy plants are desired, pinch off the terminal (end) buds on tall growing varieties when the plants reach 1’ tall. This will encourage branching. If fewer but larger flowers are desired instead, pinch off all flower buds except the terminal ones. Stake the plant, give it room to grow and be extra sure to keep it watered and fed.
Dahlias are only hardy in zones 8-10. In zone 8, apply a protective layer of mulch in late fall for added protection. If you live in zone 7 or colder, you can either treat them as an annual or dig up the tubers if you wish to grow them again next year. After the first light frost, carefully dig them up, being sure to not damage the tubers. Cut the stalks back to a few inches, shake off excess soil, and turn the clumps upside down to dry for a few days in a frost-free location. Store in a cool, dry area between 36 and 50°F. You may store them in boxes filled with barely moist vermiculite or sand, or in paper bags, newspaper or plastic bags with plenty of air holes punched in. Once a month, check for signs of rot or drying out. Discard any rotting tubers and mist any shriveling tubers with water or pack them in slightly damp peat.